Effects of an rf phase feedback system on the coherent tunes and damping rates

One possible feedback system, designed mainly for damping the longitudinal dipole oscillations, utilizes a beam position monitor and an rf cavity. The horizontal displacement of the beam is measured at the monitor and the measurement is sent to the rf cavity. The phase of the cavity voltage is then adjusted so that an electron changes its energy by the additional amount of ..delta../var epsilon/ = /zeta/E/sub o/x/sub monitor/. This FB system introduces damping or anti-damping to the horizontal betatron oscillation and the longitudinal synchrotron oscillation. Although approximate expressions for the associated damping constants ..cap alpha../sub x,s/ can be obtained by elementary considerations, it is perhaps constructive to have an exact calculation available as well. In the following, we will describe the exact calculation; obtain approximate expressions of ..cap alpha../sub x,s/ from the exact calculation; obtain approximate expressions of ..delta nu../sub x,s/, the coherent tune shifts caused by the FB systems; and numerically compare the exact and approximate results under various conditions. We assume that there is only one active rf cavity in the storage ring and that the monitor signal reaches the rf cavity before the beam completes one turn. 5 refs., 6 figs

On wakefields with two-dimensional planar geometry

In order to reach higher acceleration gradients in linear accelerators, it is advantageous to use a higher accelerating RF frequency, which in turn requires smaller accelerating structures. As the structure size becomes smaller, rectangular structures become increasingly interesting because they are easier to construct than cylindrically symmetric ones. One drawback of small structures, however, is that the wakefields generated by the beam in such structures tend to be strong. Recently, it has been suggested that one way of ameliorating this problem is to use rectangular structures that are very flat and to use flat beams. In the limiting case of a very flat planar geometry, the problem resembles a purely two-dimensional (2-D) problem, the wakefields of which have been studied

Aspects of Soft and Spontaneous CP Violation

We study four different models for CP violation: the standard (KM) model, the aspon model of spontaneous breaking and two models of soft breaking. In all except the standard model, the strong CP problem is addressed and solved. Testable predictions for the area of the unitarity triangle and for (epsilon'/epsilon)_K are emphasized. The issue of CP violation may well become the first place where the standard model of particle theory is shown definitively to be deficient. There are two reasons for expecting this to happen: (1) the strong CP problem is still not understood in the unadorned standard model and (2) the KM mechanism, although unquestionably present, may not provide the full explanation of epsilon_K and (epsilon'/epsilon)_K.Comment: 24 pages LaTeX including 4 figures. Minor modification to analysis of lower bound for d_n, summarized in new Table I

Effect of Parametric Resonances on the Bunched-beam Dilution Mechanism

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Enterohemorrhagic Escherichia coli O157: H7 from healthy dairy cattle in Mid-West Brazil: occurrence and molecular characterization

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 represents the major Shiga toxin-producing E. coli (STEC) strain related to large outbreaks and severe diseases such as hemorrhagic colitis (HC) and the potentially lethal hemolytic uremic syndrome (HUS). The aim of this study was to report the occurrence and molecular characterization of O157:H7 isolates obtained by rectal swab from 52 healthy dairy cattle belonging to 21 farms in Mid-West of Brazil. Detection of 16SrRNA, stx1, stx2, rfbO157, fliCh7, eae, ehxA, saa, cnf1, chuA, yjaA and TSPE4.C2 genes was performed by PCR. The isolates were further characterized by serotyping. Two hundred and sixty E. coli isolates were obtained, of which 126 were characterized as STEC. Two isolates from the same cow were identified as serotype O157:H7. Both isolates presented the stx2, eae, ehxA, saa and cnf1 virulence factor genes and the chuA gene in the phylogenetic classification (virulent group D), suggesting that they were clones. The prevalence of O157:H7 was found to be 1.92% (1/52 animals), demonstrating that healthy dairy cattle from farms in the Mid-West of Brazil are an important reservoir for highly pathogenic E. coli O157:H7

Limit Cycle Instability of Proton Beams Generated by Nonlinear Electron-Cooling Force

This research was sponsored by the National Science Foundation Grant NSF PHY-931478